1. We have constructed a cDNA clone complementary to the 5' terminal portion of the rat type II collagen mRNA. This clone contains a 521 bp cDNA insert including 153 bp of the 5' untranslated region plus 368 bp coding for the signal peptide, the amino propeptide and a part of the telopeptide. 2. We have isolated several genomic clones which contain the 5' terminal portion of the rat type II procollagen gene. We determined the nucleotide sequence of the promoter and the first exon of the gene. 3. We have constructed a cDNA clone coding for the mouse pro Alphal type IV collagen chain. DNA sequence analysis showed that the globular domain of the pro Alphal(IV) chain is composed of 273 amino acids. 4. We have isolated several overlapping genomic clones which span about 40 kb and contain much of the mouse pro Alphal(IV) collagen gene chain. The coding region of this gene is subdivided into many small exons, roughly similar in size and each estimated to be about 170 bp. Sequencing of one of the exons shows it to be 178 bp in length and to code for a helical segment of the protein. The difference in exon size for helical domains between the pro Alphal(IV) and the chains for types I, II and III collagen suggest that this basement membrane gene evolved independently of the interstitial collagen genes. 5. We have isolated almost the complete human type II collagen gene.